U.S. forecasters say Tropical Storm Beta is strengthening as it churns off the coast of Central America and is likely to become a hurricane later Friday.

The National Weather Service says hurricane warnings are in effect for the Colombian islands of San Andres and Providencia, as the slow-moving storm churns 60 kilometers east of San Andres.

Beta is the record 23rd named storm of this year's Atlantic hurricane season. It is moving toward the north at six kilometers per hour.

Forecasters say the center of the storm could reach mainland Nicaragua by Sunday.

The storm's maximum sustained winds are near 100 kilometers per hour and are expected to strengthen Friday. Beta is expected to dump as much as 38 centimeters of rain across Honduras, Nicaragua, San Andres and Providencia.